Conventionally, in a needle bed of a flat knitting machine, knitting needles and sinkers are alternately positioned along the longitudinal direction. A knitting loop consists of a needle loop that is formed when a knitting needle pulls down a knitting yarn and a sinker loop that is formed when a sinker holds a knitting yarn between knitting needles when the needle loop is formed. The sinker is necessary also in order to perform knock-over smoothly to let a knitting needle through a previous loop that has been already knitted, when the knitting needle is pulled into a needle bed so as to form a new knitting loop. Furthermore, when a knitting needle moves forward to a tooth portion so as to receive a fed knitting yarn at its front end portion, the sinker serves to prevent “yarn moving upward” in which a knitting loop that has been already formed goes up toward the front end portion in accordance with the movement of the knitting needle.
European Patent European Patent EP-B1 0681046, for example, discloses a sinker apparatus that can move forward to a tooth portion and press a previous loop. This European Patent Publication discloses the configuration in which a cam mechanism that is provided in a carriage moves the sinker forth into/back from the tooth portion when the carriage moves along the longitudinal direction in the needle bed. The sinker slides in a groove on an auxiliary floor that is provided above the knitting needle, and the cam mechanism controls the position of the sinker so that the sinker is not in contact with the knitting loop after the travel of the carriage. The sinker can hold its position by a frictional force in the groove in which the sinker slides, and can press a previous loop by moving forward to the tooth portion, if necessarily, after the front end portion of the knitting needle is fed with a yarn. The cam mechanism is driven by a stepping motor. The stepping motor can perform driving independently while the carriage is in motion.
In Japanese Examined Patent Publication JP-B2 5-83657(1993), for example, the applicant of the present invention discloses a sinker apparatus in a flat knitting machine in which a sinker plate that is positioned between knitting needles and that presses down a previous loop at a knitting yarn stopping portion at its front end portion can move forward to a tooth portion that is formed between the front and the rear needle beds by a force of a spring. Since previous loops are pulled down each by each, such a sinker apparatus with a force of a spring can reliably apply a pulling down force to knitting stitches even when a knitting operation is performed so that a pulling down force is not applied uniformly to the entire a knitting fabric. When a greater force than a force of a spring to the sinker plate is applied to a knitting yarn, the front end portion of the sinker plate can automatically move back from the tooth portion, so that too strong a force is not applied to the knitting yarn. The apparatus is also provided with a cam mechanism that automatically moves the sinker plate back from the tooth portion when a knitting needle is fed with a knitting yarn.
In Japanese Unexamined Patent Publication JP-A 9-31806(1997), the applicant of the present invention also discloses a movable sinker apparatus that performs an operation to press a previous loop by applying a force of a spring to a sinker plate, and an operation to hold the sinker plate at a rest position where the sinker plate is withdrawn from a tooth portion by a cam mechanism for switching of the operation between holding at the rest position and releasing the sinker plate, which is provided in a carriage. For example, when knitting with a thick knitting yarn, there is a possibility that a knitting yarn stopping portion of the sinker plate may scratch a knitting fabric in a racking operation that causes relative movements of the front and the rear needle beds in the longitudinal direction when the sinker plate is constantly at the tooth portion in order to press a previous loop. In order to prevent this possibility, the sinker plate is held at the rest position in which the sinker plate is withdrawn from the position where the front end portion presses a previous loop at the tooth portion, after the travel of the carriage. An swing plate for locking is provided in the needle bed as a mechanism that holds the sinker plate at the rest position by resisting the spring force. A cam for controlling the sinker that is provided in the carriage swings the swing plate for locking, so that the sinker plate is held at the rest position or released. The cam mechanism that is provided in the carriage also forces the sinker plate to be withdrawn to the rest position when a knitting needle is fed with a knitting yarn.
The sinkers to which a force of a spring is not applied such as disclosed in European Patent EP-B1 0681046 are not capable of pulling down a knitting fabric sufficiently for each knitting stitch. In the sinkers that press down a previous loop by a force of a spring such as disclosed in Japanese Examined Patent Publication JP-B2 5-83657(1993) and Japanese Unexamined Patent Publication JP-A 9-31806(1997), after a sinker plate is withdrawn from a tooth portion at a position where a knitting needle is fed with a yarn, a sinker plate to which a force of a spring is applied returns to the state where the front end portion presses down a previous loop. Since this sinker plate returns while a force of a spring is applied, the front end portion of the sinker plate hits a knitting yarn of a previous loop. For example, when a binding stitch treatment that narrows the width of a knitting fabric is performed a carriage needs to move back and forth a plurality of times in order to knit one course. In this procedure, a new knitting loop is not formed even by the travel of the carriage, and the front end portion of the sinker plate repeats to press down and release a previous loop with respect to the knitting needle that simply holds the knitting stitch that has been already knitted. When the front end portion of the sinker plate repeatedly hits a knitting yarn, “yarn thinning” in which a yarn is stretched to be thin, and “nap” in which the fiber of a knitting yarn is loosened are likely to occur, depending on the characteristics of the knitting yarn. When a knitting yarn is worn out by “yarn thinning,” “nap,” or the like, the texture of the knitting fabric is damaged.